title: The genomic distribution of sex-biased genes in drosophila serrata: X chromosome demasculinization, feminization, and hyperexpression in both sexes.
abstract: The chromosomal distribution of genes with sex-biased expression is often nonrandom, and in species with XY sex chromosome systems, it is common to observe a deficit of X-linked male-biased genes and an excess of X-linked female-biased genes. One explanation for this pattern is that sex-specific selection has shaped the gene content of the X. Alternatively, the deficit of male-biased and excess of female-biased genes could be an artifact of differences between the sexes in the global expression level of their X chromosome(s), perhaps brought about by a lack of dosage compensation in males and hyperexpression in females. In the montium fruit fly, Drosophila serrata, both these explanations can account for a deficit of male-biased and excess of female-biased X-linked genes. Using genome-wide expression data from multiple male and female tissues (n = 176 hybridizations), we found that testis- and accessory gland-specific genes are underrepresented whereas female ovary-specific genes are overrepresented on the X chromosome, suggesting that X-linkage is disfavored for male function genes but favored for female function genes. However, genes with such sex-specific functions did not fully account for the deficit of male-biased and excess of female-biased X-linked genes. We did, however, observe sex differences in the global expression level of the X chromosome and autosomes. Surprisingly, and in contrast to other species where a lack of dosage compensation in males is responsible, we found that hyperexpression of X-linked genes in both sexes leads to this imbalance in D. serrata. Our results highlight how common genomic distributions of sex-biased genes, even among closely related species, may arise via quite different evolutionary processes.
authors.affiliation: The School of Biological Sciences, The University of Queensland, St Lucia, Australia.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Allen
authors.forename: Russell
authors.initials: R
authors.lastname: Bonduriansky
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Chenoweth
mesh_terms: D000818:Animals; D004303:Dosage Compensation, Genetic; D004330:Drosophila / Q000235:genetics*; D005260:Female; D005262:Feminization / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D050172:Genes, X-Linked; D023281:Genomics; D008297:Male; D012727:Sex Characteristics; D019849:Sex Determination Processes; D014960:X Chromosome / Q000235:genetics*
keywords: Drosophila; X chromosome; dosage compensation; sex-biased gene expression